Pyrimidinoceptors-mediated activation of Ca 2+-dependent Cl − conductance in mouse endometrial epithelial cells

Abstract

Previous studies have demonstrated the activation of endometrial Cl − secretion through P 2Y2 (P 2U) purinoceptors by extracellular ATP. The present study further explored the presence of pyrimidine-sensitive receptors in the primary cultured mouse endometrial epithelial cells using the short-circuit current ( I SC) and whole-cell patch-clamp techniques. UDP induced a transient increase in I SC in a concentration-dependent manner (EC 50≈8.84 μM). The UDP-induced I SC was abolished after pretreating the epithelia with a calcium chelator, 1,2-bis-(2-aminophenoxy)-ethane- N, N, N′ N′tetraacetic acid-acetomethyl ester (BAPTA-AM), suggesting the dependence of the I SC on cytosolic free Ca 2+. The type of receptor involved was studied by cross-desensitization between ATP and UDP. ATP or UDP desensitized its subsequent I SC response. However, when ATP was added after UDP, or vice versa, a second I SC response was observed, indicating the activation of distinct receptors, possibly pyrimidine-sensitive receptors in addition to P 2Y2 (P 2U) receptors. Similar results were observed in the patch-clamp experiments where UDP and ATP were shown to sequentially activate whole-cell current in the same cell. The UDP-activated whole-cell current exhibited outward rectification with delay activation and inactivation at depolarizing and hyperpolarizing voltages, respectively. In addition, the UDP-evoked whole-cell current reversed near the equilibrium potential of Cl − in the presence of a Cl − gradient across the membrane, and was sensitive to 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS), indicating the activation of Ca 2+-activated Cl − conductance. These characteristics were very similar to that of the ATP-activated whole-cell current. Taken together, our findings indicate the presence of distinct receptors, pyrimidinoceptors and P 2Y2 (P 2U) receptors in mouse endometrial epithelial cells. These distinct receptors appear to converge on the same Ca 2+-dependent Cl − channels.